The present invention relates to wireless communications system, and more particularly, to receiver apparatus, methods and computer program products.
Wireless communications are now widely used for a variety of applications, including voice telephony and data communications applications, such as wireless e-mail and internet applications. As the number of wireless applications has increased, the data rate requirements associated with these applications has generally increased. Accordingly, new higher data rate wireless communications standards, and modifications to existing standards that can provide increased data rates, have been proposed.
For example, Enhanced Data rates for Global Evolution (EDGE) has been introduced to increase potential data rates in systems conforming to the Global System for Mobile Communications/General Packet Radio Service (GSM/GPRS) standards. Although GPRS and EDGE share the same symbol rate, the modulation bit rate differs. In particular, GSM has traditionally employed Gaussian Minimum Shift Keying (GMSK), which may be considered a type of phase modulation. Every symbol that is transmitted represents one bit, i.e., each shift in the phase represents one bit. EDGE is specified to reuse the channel structure, channel width, channel coding and the existing mechanisms and functionality of GPRS. However, EDGE uses 8-phase shift keying (8-PSK), which has the similar qualities in terms of generating interference on adjacent channels as GMSK, but can provide a higher data rate. 8-PSK modulation is a linear modulation in which three consecutive bits are mapped onto one symbol in the I/Q plane. The symbol rate, or the number of symbols sent within a certain period of time, remains the same as for GMSK, but each symbol represents three bits instead of one, which can increase the total data rate by a factor of three.
Co-channel interference, i.e., interference arising from frequency reuse in a geographical area, may limit user capacity and signal quality in a cellular system. A technique for dealing with co-channel interference between GMSK signals is described in U.S. patent application Ser. No. 09/549,559, entitled “Method and Apparatus for Interference Rejection,” to Khayrallah et al., filed Apr. 14, 2000, and in U.S. patent application Ser. No. 09/956,443, entitled “Methods and Apparatus for Canceling Co-channel Interference in a Receiving System Using Spatio-Temporal Whitening,” to Arslan et al., filed Sep. 19, 2001. Other techniques are described in Published PCT International Application No. WO98/16021.
These techniques may not be useful when 8-PSK modulation is used for the desired signal. Interference suppression for 8-PSK modulated desired signals has been proposed for receivers having multiple antennas, but it may be undesirably costly to use multiple antennas in a mobile terminal.